Use of δ18Oatm in dating a Tibetan ice core record of Holocene/Late Glacial climate.

Ice cores from the northwestern Tibetan Plateau (NWTP) contain long records of regional climate variability, but refrozen meltwater and dust in these cores has hampered development of robust timescales. Here, we introduce an approach to dating the ice via the isotopic composition of atmospheric O2 in air bubbles (δ18Oatm), along with annual layer counting and radiocarbon dating. We provide a robust chronology for water isotope records (δ18Oice and d-excess) from three ice cores from the Guliya ice cap in the NWTP. The measurement of δ18Oatm, although common in polar ice core timescales, has rarely been used on ice cores from low-latitude, high-altitude glaciers due to (1) low air pressure, (2) the common presence of refrozen melt that adds dissolved gases and reduces the amount of air available for analysis, and (3) the respiratory consumption of molecular oxygen (O2) by micro-organisms in the ice, which fractionates the δ18O of O2 from the atmospheric value. Here, we make corrections for melt and respiration to address these complications. The resulting records of water isotopes from the Guliya ice cores reveal climatic variations over the last 15,000 y, the timings of which correspond to those observed in independently dated lake and speleothem records and confirm that the Guliya ice cap existed before the Holocene. The millennial-scale drivers of δ18Oice are complex and temporally variable; however, Guliya δ18Oice values since the mid-20th century are the highest since the beginning of the Holocene and have increased with regional air temperature.

Early atmospheric contamination on the top of the Himalayas since the onset of the European Industrial Revolution.

Because few ice core records from the Himalayas exist, understanding of the onset and timing of the human impact on the atmosphere of the "roof of the world" remains poorly constrained. We report a continuous 500-y trace metal ice core record from the Dasuopu glacier (7,200 m, central Himalayas), the highest drilling site on Earth. We show that an early contamination from toxic trace metals, particularly Cd, Cr, Mo, Ni, Sb, and Zn, emerged at high elevation in the Himalayas at the onset of the European Industrial Revolution (∼1780 AD). This was amplified by the intensification of the snow accumulation (+50% at Dasuopu) likely linked to the meridional displacement of the winter westerlies from 1810 until 1880 AD. During this period, the flux and crustal enrichment factors of the toxic trace metals were augmented by factors of 2 to 4 and 2 to 6, respectively. We suggest this contamination was the consequence of the long-range transport and wet deposition of fly ash from the combustion of coal (likely from Western Europe where it was almost entirely produced and used during the 19th century) with a possible contribution from the synchronous increase in biomass burning emissions from deforestation in the Northern Hemisphere. The snow accumulation decreased and dry winters were reestablished in Dasuopu after 1880 AD when lower than expected toxic metal levels were recorded. This indicates that contamination on the top of the Himalayas depended primarily on multidecadal changes in atmospheric circulation and secondarily on variations in emission sources during the last 200 y.

Amino acid polymorphisms in the fibronectin-binding repeats of fibronectin-binding protein A affect bond strength and fibronectin conformation.

The Staphylococcus aureus cell surface contains cell wall-anchored proteins such as fibronectin-binding protein A (FnBPA) that bind to host ligands (e.g. fibronectin; Fn) present in the extracellular matrix of tissue or coatings on cardiac implants. Recent clinical studies have found a correlation between cardiovascular infections caused by S. aureus and nonsynonymous SNPs in FnBPA. Atomic force microscopy (AFM), surface plasmon resonance (SPR), and molecular simulations were used to investigate interactions between Fn and each of eight 20-mer peptide variants containing amino acids Ala, Asn, Gln, His, Ile, and Lys at positions equivalent to 782 and/or 786 in Fn-binding repeat-9 of FnBPA. Experimentally measured bond lifetimes (1/koff) and dissociation constants (Kd = koff/kon), determined by mechanically dissociating the Fn·peptide complex at loading rates relevant to the cardiovascular system, varied from the lowest-affinity H782A/K786A peptide (0.011 s, 747 µm) to the highest-affinity H782Q/K786N peptide (0.192 s, 15.7 µm). These atomic force microscopy results tracked remarkably well to metadynamics simulations in which peptide detachment was defined solely by the free-energy landscape. Simulations and SPR experiments suggested that an Fn conformational change may enhance the stability of the binding complex for peptides with K786I or H782Q/K786I (Kdapp = 0.2-0.5 µm, as determined by SPR) compared with the lowest-affinity double-alanine peptide (Kdapp = 3.8 µm). Together, these findings demonstrate that amino acid substitutions in Fn-binding repeat-9 can significantly affect bond strength and influence the conformation of Fn upon binding. They provide a mechanistic explanation for the observation of nonsynonymous SNPs in fnbA among clinical isolates of S. aureus that cause endovascular infections.

Incorporation and exclusion of long chain alkyl halides in fatty acid monolayers at the air-water interface.

Mixed monolayers of deuterated palmitic acid C(15)D(31)COOH (dPA) and deuterated stearic acid C(17)D(35)COOH (dSA) with 1-bromoalkanes of different alkyl chain length (C(4) to C(16)) at the air-water interface were investigated. Alkanes and 1-chlorohexadecane ClC(16)H(33) (ClHex) were also studied to compare the effects of the halogen on the mixed monolayers. Surface pressure-area isotherms and Brewster angle microscopy (BAM) were used to obtain the organization and phase behavior, providing a macroscopic view of the mixed monolayers. A molecular-level understanding of the interfacial molecular organization and intermolecular interactions was obtained by using vibrational sum frequency generation (SFG) spectroscopy and infrared reflection-absorption spectroscopy (IRRAS). It was found that from the alkyl halide molecules investigated 1-bromopentadecane, BrC(15)H(31) (BrPent), 1-bromohexadecane, BrC(16)H(33) (BrHex), and ClHex incorporate into the fatty acid monolayers. Alkanes of 15- and 16-carbon chain length do not incorporate into the fatty acid monolayer, which suggests that the halogen is needed for incorporation. Isotherms and spectra suggest that BrHex molecules are squeezed out, or excluded, from the fatty acid monolayer as the surface pressure is increased, while BAM images confirm this. Additionally, SFG spectra reveal that the alkyl chains of both fatty acids (dPA and dSA) retain an all-trans conformation after the incorporation of alkyl halide molecules. BAM images show that at low surface pressures BrHex does not affect the two-dimensional morphology of the dPA and dSA domains and that BrHex is miscible with dPA and dSA. We also present for the first time BAM images of BrHex deposited on a water surface, which reveal the formation of aggregates while the surface pressure remains unchanged from that of neat water.

Surface residence and uptake of methyl chloride and methyl alcohol at the air/water interface studied by vibrational sum frequency spectroscopy and molecular dynamics.

Vibrational sum frequency generation (VSFG) spectroscopy and molecular dynamics (MD) simulations are used to study the surface residence and organization of gas-phase methyl halide and methyl alcohol molecules adsorbed to the air/water interface, while Raman spectroscopy is used to detect the uptake of the gas-phase species into the bulk aqueous phase. Spectroscopy results reveal the presence of methyl alcohol in the bulk and at the surface. Methyl chloride is detected in the bulk, but not at the surface. This indicates that methyl alcohol adsorbs to the aqueous surface in a layer that is ordered, in agreement with previous studies, and is also readily taken up into the bulk aqueous phase, whereas methyl chloride adsorbs, but, while being taken up into the bulk liquid, has lower surface number density and/or forms a more disordered surface layer than methyl alcohol. MD simulations show that methyl halide molecules transition readily between the gas phase and interface, resulting in significantly shorter residence times at the surface for the methyl halides relative to methyl alcohol. Both the geometries that the methyl species adopt at the interface and the interactions between the methyl species and the interfacial water molecules differ for the halides and the alcohol. Complementary studies of butyl species show similar results: butyl alcohol adsorbs to the aqueous surface in a layer that exhibits a certain degree of order corresponding to the chains aligned along the surface normal, while a markedly more disordered surface layer and shorter residence times are observed in MD simulations for the butyl halides as compared to the alcohol. Desorption from the interface was found to be less frequent for the butyl halides than for the methyl halides by MD simulations. Although Raman studies show uptake of the butyl alcohol into the bulk phase, neither Raman studies nor MD simulations provide any evidence for uptake of the butyl halides into the bulk phase. The profound difference in preferred orientations between alkyl halides and alcohols at the aqueous surface, with the halogen atom of the alkyl halides being to a large degree exposed to the vapor phase, is likely to have consequences for chemistry of alkyl halides adsorbed on the surface of atmospheric aerosol particles.

Central Tibetan Plateau atmospheric trace metals contamination: A 500-year record from the Puruogangri ice core.

A ~500-year section of ice core (1497-1992) from the Puruogangri ice cap has been analyzed at high resolution for 28 trace elements (TEs: Ag, Al, As, Ba, Bi, Cd, Co, Cr, Cs, Cu, Fe, Ga, Li, Mg, Mn, Na, Nb, Ni, Pb, Rb, Sb, Sn, Sr, Ti, Tl, U, V and Zn) to assess different atmospheric contributions to the ice and provide a temporal perspective on the diverse atmospheric influences over the central Tibetan Plateau (TP). At least two volcanic depositions have significantly impacted the central TP over the past 500years, possibly originating from the Billy Mitchell (1580, Papua New Guinea) and the Parker Peak (1641, Philippines) eruptions. A decreasing aeolian dust input to the ice cap allowed the detection of an atmospheric pollution signal. The anthropogenic pollution contribution emerges in the record since the early 1900s (for Sb and Cd) and increases substantially after 1935 (for Ag, Zn, Pb, Cd and Sb). The metallurgy (Zn, Pb and steel smelting) emission products (Cd, Zn, Pb and Ag) from the former Soviet Union and especially from central Asia (e.g., Kyrgyzstan, Kazakhstan) likely enhanced the anthropogenic deposition to the Puruogangri ice cap between 1935 and 1980, suggesting that the westerlies served as a conveyor of atmospheric pollution to central Tibet. The impact of this industrial pollution cumulated with that of the hemispheric coal and gasoline combustion which are respectively traced by Sb and Pb enrichment in the ice. The Chinese steel production accompanying the Great Leap Forward (1958-1961) and the Chinese Cultural Revolution (1966-1976) is proposed as a secondary but proximal source of Pb pollution affecting the ice cap between 1958 and 1976. The most recent decade (1980-1992) of the enrichment time series suggests that Puruogangri ice cap recorded the early Sb, Cd, Zn, Pb and Ag pollution originating from developing countries of South (i.e., India) and East (i.e., China) Asia and transported by the summer monsoonal circulation.

Shedding light on water structure at air-aqueous interfaces: ions, lipids, and hydration.

An account is given of the current state of understanding of aqueous salt, acid, and lipid/water surfaces, interfacial depth, and molecular organization within the air-solution interfacial region. Water structure, hydration, surface propensity of solutes, and surface organization are discussed. In this perspective, vibrational sum frequency generation spectroscopic studies of aqueous surfaces are interpreted. Comment on future directions within the field of aqueous surface structure is provided.